The invention relates to a method and apparatus for depositing a layer of aggregate material of approximately consistent depth over a large area of land. While the invention may be utilized in laying down a layer of sand or gravel for constructing a large parking lot or other large construction site in an economical manner, the invention has particular utility and provides particular advantages in preparing a new land fill waste-disposal site economically and in an environmentally responsible manner. Other applications for the present invention may be found in any task where aggregate material is to be deposited over a site containing areas which must not be subjected to heavy loads or where features of the terrain such as deep ditches or the like must be spanned or otherwise dealt with. Another possible application is surface mine reclamation where large quantities of aggregate material such as soil materials must be spread over a large area economically.
In the case of preparing a large area of land for a new land fill waste-disposal site, it is common to deposit over the entire site a first layer of sealing clay, then a layer of sand, another layer of clay and over these deposited layers the entire site is covered with a plastic liner of, for example, high-density polyethylene to prevent as much as possible liquids from the waste from leaching into the land and possibly contaminating underground water. Over the plastic liner a leachate collection system is located consisting of perforated plastic pipe immediately surrounded by a filter fabric and rock. The land is graded so that liquid will flow over the plastic liner to the leachate collection system where it is collected and properly disposed of. It is then conventional to deposit a layer of sand of about twelve to about eighteen inches in depth over the entire plastic liner and leachate collection system and thus over the entire land fill site. Conventional methods of laying down a layer of aggregate such as the sand are not well suited to this job. For example, a loaded dump truck moving across the plastic while depositing a trailing stream of sand can be quite destructive to the plastic liner. Even if the dump truck were to back over the sand as it is deposited from the rear of the truck, the massive weight of the truck may present problems to the integrity of the plastic liner and a slight detour from the proper path would lead the truck directly onto the liner.
Another conventional method is to dump the sand at the edge of the site and have a bull dozer spread the sand over the liner such that the dozer always tracks over sand which it has pushed ahead and spread. This method is disadvantageous in that it is very difficult to economically produce a layer of sand of consistent depth and the heavy equipment required, and the number of passes required, increase the probability of plastic liner and leachate collection system degradation. Also the great weight of the sand piles initially being shifted across areas of the liner may cause tearing of the liner. A great degree of operator skill would also be necessary. Further, in order to perform the conventional methods using large dump trucks and bulldozers, large numbers of expensive man-hours must be expended as well as the use of large numbers of very expensive heavy machinery. Due to the large number of men and machines used in conventional methods scheduling of truck arrivals and equipment usage can be an extremely important part of the job causing heightened probabilities of down time and wasted machine-hours and man-hours. As compared to the present invention, conventional methods may also use a greater amount of fuel.